I. Field of the Invention
The present invention relates to telecommunications, and more particularly, to wireless communications.
II. Description of the Related Art
Wireless communications systems provide wireless service to a number of wireless or mobile units situated within a geographic region. The geographic region supported by a wireless communications system is divided into spatially distinct areas commonly referred to as “cells.” Each cell, ideally, may be represented by a hexagon in a honeycomb pattern. In practice, however, each cell may have an irregular shape, depending on various factors including the topography of the terrain surrounding the cell. Moreover, each cell can be further broken into two or more sectors. Each cell is commonly divided into three sectors, each having an angular span of 120 degrees.
A conventional cellular system comprises a number of cell sites or base stations geographically distributed to support the transmission and reception of communication signals to and from the wireless or mobile units. Each cell site handles voice communications within a cell. Moreover, the overall coverage area for the cellular system may be defined by the union of cells for all of the cell sites, where the coverage areas for nearby cell sites overlap to ensure, where possible, contiguous communication coverage within the outer boundaries of the system's coverage area.
Each base station comprises at least one radio and at least one antenna for communicating with the wireless units in that cell. Moreover, each base station also comprises transmission equipment for communicating with a Mobile Switching Center (MSC). A mobile switching center is responsible for, among other things, establishing and maintaining calls between the wireless units, between a wireless unit and a wireline unit through a public switched telephone network (PSTN), as well as between a wireless unit and a packet data network (PDN), such as the Internet. A base station controller (BSC) administers the radio resources for one or more base stations and relays this information to the MSC.
When active, a wireless unit receives signals from at least one base station or cell site over a forward link or downlink and transmits signals to at least one cell site or base station over a reverse link or uplink. There are many different schemes for defining wireless links or channels for a cellular communication system. These schemes include, for example, TDMA (time-division multiple access), FDMA (frequency-division multiple access), and CDMA (code-division multiple access) schemes.
In a CDMA scheme, each wireless channel is distinguished by a distinct channelization code (e.g., spreading code, spread spectrum code or Walsh code) that is used to encode different information streams. These information streams may then be modulated at one or more different carrier frequencies for simultaneous transmission. A receiver may recover a particular stream from a received signal using the appropriate Walsh code to decode the received signal.
Each base station using a spread spectrum scheme, such as CDMA, offers a number of Walsh codes, and consequently, can serve a corresponding number of users, within each sector of a cell. In the CDMA 2000 3G-1X system, for example, the number of Walsh codes made available by each sector for voice may be defined by the radio configuration (“RC”) employed by the base station. The maximum number of Walsh codes available for an RC3 assignment is 64, while RC4 assignment, in contrast, supports a maximum of 128 Walsh codes. Under certain conditions, such as when the majority of users are in benign RF environment, the users are concentrated in the area near antenna or majority of the users are stationary, etc., the RF capacity of CDMA 2000 3G-1X may exceed the Walsh code capability of RC3 (radio configuration 3) assignment. An RC3 assignment may be expected to be exceeded when technologies, such as transmit diversity, an intelligent antenna(s), and/or a selectable mode vocoder(s) are introduced.
The number of Walsh codes made available by a base station may take into consideration variables including the transmit power requirements associated with the selected radio configuration. For example, an RC4 assignment typically requires a relatively longer spreading code and may have a greater transmit power requirement than an RC3 assignment, which is a relatively shorter spreading code. Consequently, a tradeoff exists between the power efficiency of the base station based on the RC configuration employed and the length/number of spreading codes made available within each sector of a cell. An RC4 assignment, for example, may degrade capacity by supporting a weaker coding rate than an RC3 assignment.
With the explosion of the Internet and the increasing demand for data, resource management has become a growing issue in cellular communication systems. Next generation wireless communication systems are expected to provide high speed data services in support of Internet access and multimedia communication. Unlike voice, however, data communications may be relatively delay tolerant and potentially bursty. Data communications, as such, may not require dedicated links on the downlink or the uplink, as is the case with voice communication through the use of the fundamental channel, but rather enable one or more supplemental channels for a short duration using resources that could be shared by a number of wireless units. By this arrangement, each of the wireless units competes for available resources. The resources to be managed on the downlink include transmit power and Walsh codes.
As data communications are typically shorter in time duration than voice communication, next generation wireless communication systems are expected to use channel bursts to maximize data transfer. Unlike voice channels, however, these channel bursts—commonly referred to as data bursts—are designed for the supplemental channel. A data burst, for the purposes of the present disclosure, may correspond with the sending of a signaling message(s) over a fundamental channel specifying the length of time and data rate at a particular radio configuration in which a supplemental channel may be set up for such data transmission. Consequently, data bursts rely on the availability of a supplemental channel. The supplemental channel, however, may use more sector resources, such as power and Walsh codes, than the fundamental channel. As such, the supplemental channel may take a lower priority in support of data communication, in comparison with the fundamental channel in support of voice communication.
In view of the above considerations, a method is needed for assigning Walsh codes and power to the supplemental channel in support of the use of a data burst(s). Since different Radio Configurations specified in the standard allow for trading off power and Walsh code resources, a method is also needed for an optimal selection of Radio Configurations in support of a data burst(s).